Estimation of average energy consumption of ripple-carry adder based on average length carry chains

We show theoretically that the average energy consumption of a ripple-carry adder is O(W), and the upper bound on the average energy consumption is O(Wlog/sub 2/W), where W is the word-length of the operands. Our theoretical analysis is based on a simple state transition diagram (STD) model of a full adder cell and the observations that the average length of a carry propagation chain is v=2, and the average length of the maximum carry chain is v/spl les/log/sub 2/W. To verify our theoretical conclusions, we use the HEAT CAD tool to estimate the average power consumed by the ripple-carry adder for word-lengths 4/spl les/W/spl les/64. The experimental results show that, for W/spl ges/16, the error in our theoretical estimations is around 15%.